This invention relates to fork positioners for adjusting the transverse spacing between load-lifting forks of a lift-truck, and to side-shifters for moving the forks transversely in unison. More particularly, the invention relates to a fork positioner for a lift truck side-shifting carriage which is compatible with standard forks and which does not require any structure protruding forwardly beyond the forward extremities of the upstanding portions of the forks, so as to maximize the counterbalanced load-lifting capacity of the lift truck.
Various types of fork positioners have been employed in the past to enable a lift truck operator to selectively adjust the transverse spacing between load-lifting forks for engaging different types of loads. Most of these have required the substitution of special load carriages with special forks for the standard carriage and forks of the lift truck, as exemplified by the following U.S. Pat. Nos.: 1,813,596; 2,451,943; 2,483,745; 2,748,966; 3,424,328; 4,335,992; and 4,381,166. Some, such as that shown in U.S. Pat. No. 4,280,781, also include a side-shifting function. However, the requirement for complete replacement of the standard carriage and forks of the lift truck makes such devices unduly expensive and time-consuming to install and remove.
On the other hand, some fork positioners are adapted to be mounted on a standard carriage compatibly with the standard forks, as shown in U.S. Pat. No. 4,688,982 and the following Japanese patent publication Nos.: 53-61982; 53-079673; 54-120075; 56-121095; 56-140595. However, these positioners do not provide side-shifting of the forks, which is a function needed much more frequently than is fork positioning to position the forks properly with respect to a load or with respect ot a load-depositing location. Also, these devices require fork-positioning structures which protrude either forwardly of the upstanding portions of the forks or behind the upstanding portions. This necessitates additional space in a fore-and-aft direction which forces the load to protrude forwardly of the front axle of the truck to an excessive degree, detracting from the load-lifting capacity of a counterbalanced lift truck.
Some fork positioners provide an intermediate fork-positioning carriage adaptable to mount on the standard carriage of the lift truck, as shown for example in U.S. Pat. No. 2,339,120 and the following West German patent publications: 2853109; 2929712; 3301595. Some of these carriages provide a side-shifting function in addition to fork positioning. However, these devices either require special forks which add to their expense, or likewise force the load to protrude forwardly of the front axle of the truck to an excessive degree.
Accordingly, what is needed is a fork positioner for a forklift truck which is compatible with the truck's standard forks and yet does not require excessive forward protrusion of the load to create space for the fork positioning mechanism.